Did you read the
instructions about installing an extension in OO?
Apart from the ways listed there you can use unopkg (located in the OO program directory where soffice, swriter are located):
Code:
unopkg add /path/to/dictionary.oxt
The installed dictionaries for a user are located in ~/.openoffice.org/3/user/uno_packages/cache/uno_packages/<random charactes>/<dict name>
Dictionaries installed by root are located in /opt/openoffice.org3/share/uno_packages/cache/uno_packages/<random characters>/<dict name>